Attention has been paid to carbon nanotube electrodes as electrodes or electric wires for dye-sensitized solar cells, lithium ion secondary batteries, lithium ion capacitors, electric double layer capacitors, fuel cells and the like, since these electrodes have excellent conductivity.
In dye-sensitized solar cells in particular, there are increasing expectations for carbon nanotube electrodes since these electrodes exhibit a performance comparable to platinum electrodes.
The carbon nanotubes of a carbon nanotube electrode are usually obtained by growing carbon nanotubes by chemical vapor deposition on the catalyst of a structure for forming carbon nanotube that is formed by supporting a catalyst on a substrate. Here, from the viewpoint of enhancing the performance of the electrode, it is preferable that the carbon nanotubes be long. Furthermore, from the viewpoint of enhancing the productivity of carbon nanotubes, it is preferable that the amount of growth of carbon nanotubes per unit time be larger.
As a production method for carbon nanotubes involving growing of long carbon nanotubes, for example, the production method described in Patent Document 1 is known. In the production method described in Patent Document 1, for example, a structure for forming carbon nanotube in which the substrate is formed from silicon and the catalyst is formed from iron, is used. Furthermore, it has been suggested to obtain carbon nanotubes having markedly increased heights, by using an oxidizing gas when carbon nanotubes are grown, removing the carbon attached to the catalyst by means of this oxidizing gas, and thereby sustaining the activity of the catalyst.